The present invention relates generally to integrated circuits, and, more particularly, to a system for voltage regulation and monitoring in an integrated circuit.
With the advent of micron-sized integrated circuits (ICs), power and ground grid size and IR drop of the ICs are increasing. Typically, an IC is powered by a supply voltage signal that is transmitted over a power grid to various logic circuits of the IC, while a ground grid supplies a ground voltage signal to the logic circuits. Each logic circuit is connected between nodes of the power and ground grids. Different nodes of the power grid are connected to each other by way of electronic components, such as inductors, capacitors, resistors, and so on. Similarly, different nodes of the ground grid are connected to each other by way of the electronic components. The supply voltage signal is first received by the IC at a first node of the power grid, sometimes called a supply cold point. There is minimum IR drop in a first voltage level of the supply voltage signal received at the supply cold point. The supply voltage signal is transmitted through the components of the power grid, which cause IR drop in the first voltage level of the supply voltage signal. As a result, the supply voltage signal received at a second node of the power grid, i.e., a supply hot point, has a second voltage level that is less than the first voltage level by a voltage level equivalent to the IR drop at the supply hot point. Similarly, a ground voltage signal is first received by the IC at a first node of the ground grid (a ‘ground cold point’). There is minimum IR drop in a first voltage level of the ground voltage signal received at the ground cold point. The ground voltage signal is transmitted through the components of the ground grid, which cause a rise in the first voltage level of the ground voltage signal due to the IR drop. As a result, the ground voltage signal received at a second node of the ground grid, i.e., a ground hot point, has a second voltage level that is greater than the first voltage level of the ground voltage signal by a voltage level equivalent to the IR drop at the ground hot point.
Typically, the first and second voltage levels of the supply voltage signal must be within a predetermined voltage range. If the first voltage level of the supply voltage signal at the supply cold point exceeds the highest voltage level of the predetermined voltage range, reliability and aging specifications of the IC can fail, which can result in damage to the IC. Similarly, if the second voltage level of the supply voltage signal at the supply hot point is less than the lowest voltage level of the predetermined voltage range, timing of critical paths of the IC can be affected, thereby increasing functional timing of the IC. A difference between the highest and lowest voltage levels of the supply voltage signal supplied to the IC is shrinking with the decreasing size of the ICs. Hence, voltage monitoring and regulator circuits have to be included in the IC to monitor and regulate the first and second voltage levels of the supply voltage signal.
Voltage monitoring circuits, such as high voltage detectors (HVD), low voltage detectors (LVD), and power on reset (POR) monitors are included in the IC to monitor the second voltage level of the supply voltage signal at the supply hot point. The voltage monitoring circuit has a first input terminal connected to the supply hot point for receiving the supply voltage signal received at the supply hot point and a second input terminal for receiving a first reference voltage signal. The voltage monitoring circuit generates a monitor signal at its output terminal that indicates at least one of a low voltage and POR states of the IC when the second voltage level of the supply voltage signal drops below the voltage level of the first reference voltage signal. The monitor signal indicates a high voltage state of the IC when the first voltage level of the supply voltage signal exceeds the voltage level of the first reference voltage signal. During normal operation of the IC, the lowest voltage level of the predetermined voltage range must be maintained across a logic circuit connected between the supply and ground hot points. However, the first input terminal of the voltage monitoring circuit senses only the second voltage level of the supply voltage signal received at the supply hot point, so it doesn't account for the rise in the first voltage level of the ground voltage signal at the ground hot point. As a result, the voltage monitoring circuit gives a false indication of the high and low voltage states of the IC by way of the monitor signal.
One way to overcome this problem is to increase the voltage level of the first reference voltage signal of the voltage monitoring circuit by a voltage level equal to the IR drop at the ground hot point. The voltage monitoring circuit then correctly indicates the high and low voltage states of the IC as the IR drop at the ground hot point is now accounted for. However, increasing the voltage level of the first reference voltage signal increases the power consumption of the IC. Also, the IR drop at the ground hot point may change based such that the voltage level of the first reference voltage signal will have to be changed on the fly.
A voltage regulator is included in the IC to provide the supply voltage signal to the supply cold point and regulate the first and second voltage levels of the supply voltage signal within the predetermined voltage range. The voltage regulator has a first input terminal connected to the supply hot point for receiving the supply voltage signal and a second input terminal for receiving a second reference voltage signal. The voltage regulator provides the supply voltage signal having the first voltage level to the supply cold point after regulating the first voltage level based on a voltage level of the second reference voltage signal. However, the first input terminal of the voltage regulator senses only the second voltage level of the supply voltage signal received at the supply hot point, so it doesn't account for the rise in the first voltage level of the ground voltage signal at the ground hot point. As a result, the first voltage level of the supply voltage signal is incorrectly regulated and may not be within the predetermined voltage range. Moreover, due to regulator-load regulation, the first voltage level of the supply voltage signal changes when a load current of the voltage regulator changes, which increases an output spread of the voltage regulator and impacts the regulator accuracy. Thus, regulation of the first voltage level of the supply voltage signal within the predetermined voltage range is difficult.
Therefore, it would be advantageous to have an IC that includes a high precision voltage monitoring circuit and a voltage regulator circuit with very low variation in the output voltage signal.